1. Field of the Invention
The present invention relates to novel aromatic polyimidosiloxanes with excellent solubility in organic solvents and containing photosensitive groups in their main polymer chains. More specifically, the present invention relates to organic solvent-soluble photosensitive polyimidosiloxanes providing photocured products with excellent heat resistance, electrical properties and mechanical properties including flexibility, which are suitable as overcoat materials for flexible wiring boards, interlayer insulating materials, or materials for forming insulating films on solid elements and passivation films for industrial semiconductors.
2. Description of the Related Art
Overcoat materials for flexible wiring boards, interlayer insulating films for multilayer boards, materials for forming insulating films on solid elements and passivation films for industrial semiconductors, as well as interlayer insulating materials for semiconductor integrated circuits and multilayer printed wiring boards, require excellent heat resistance and insulating properties, and photosensitive heat resistant materials are being sought to meet the demand for high density and high integration.
A number of ideas have been devised for forming such insulating films of polyimides, due to their high heat resistance and insulating properties.
However, commonly used polyimides are either insoluble in solvents and have no photosensitive groups, or the polymers containing photosensitive groups are all in the form of polyimide precursors, i.e. polyamic acids, modified by amidation or esterification of the carboxylic acid, and must have the polyamic acids converted into polyimides during photocuring, or be post-baked into polyimides after photocuring.
There also exist heat-resistant photoresist compositions prepared by mixing organic solvent-soluble polyimides (without photosensitive groups) with monomers which contain a photocurable group and subjecting the mixture to photocuring (see, for example, Japanese Unexamined Patent Publication No. 54-109828), but such compositions have inferior photocuring properties, while the heat resistance of the polyimides after photocuring is insufficient. In addition, since aromatic polyimides with superior heat resistance generally have inferior solubility in solvents, they are not suitable for the formation of relief patterns which involves a step of dissolving the unexposed parts after photocuring.
Ideas have also been proposed for obtaining polyimides with excellent photosensitivity and heat resistance by reacting a tetracarboxylic dianhyride with a diamine compound containing a photocrosslinkable unsaturated double bond, such as diaminochalcone (see, for example, Japanese Unexamined Patent Publication No. 57-131227).
However, although polyimides obtained in this manner have excellent photosensitivity, their inferior solubility in organic solvents results in longer times required for dissolution, thus constituting a practicality problem for the formation of relief patterns.
Polyimidosiloxanes have also been proposed in order to obtain flexible photosensitive polyimides (Japanese Unexamined Patent Publication Nos. 2-50161, 4-252227), but since polyamic acids are used as the polymer components, high-temperature heating is necessary after patterning to accomplish imidation, thus constituting a practicality problem in that thermal damage can occur in the board.